During the past decade increasing attention has been given to the improvement of complexed Group VIII metal-containing catalysts, especially those containing rhodium, for hydrogenation and the catalysis of reactions of the Oxo type such as hydroformylation and carbonylation.
Early complexed rhodium catalysts were soluble in the reaction medium. This property brought disadvantages, especially in commercial use, because the catalysts could be separated from the reaction medium only with difficulty. Some such catalysts were also volatile to a degree such that valuable metal was lost during evaporative work-up of the reaction mixture. A popular catalyst of this period was the so-called Wilkinson's catalyst, disclosed by O'Connor and Wilkinson in J. Chem. Soc. A,2065 (1968). Wilkinson's catalyst is tris(triphenylphosphine)rhodium chloride.
Various attempts have been made to overcome the disadvantages of the soluble rhodium catalysts. For example, U.S. Pat. No. 4,102,920, commonly assigned, teaches a carbonylation process comprising the use of polydentate phosphine and arsenic complexes of rhodium. Although such catalysts are soluble, i.e., homogeneous as they are called in the art, they are possessed of lessened volatility and thus are more easily retained in the reaction mixture.
Schultz et al taught the preparation of useful insoluble, i.e., heterogenous, catalysts by impregnating active carbon with rhodium derivatives such as the nitrate and Wilkinson's catalyst, and thereafter calcining the mixture. The work was presented before the Division of Petroleum Chemistry, Inc., American Chemical Society, Boston Meeting, Apr. 9-14, 1972 (Paper p. B14).
Another approach to heterogeneous catalysts involved coordinating rhodium salts with a polymeric phosphine substrate thus conferring insolubility on the catalyst and permitting its recovery from the reaction mixture by filtration. An early contribution in this direction was made by Grubbs et al as reported in J. Amer. Chem. Soc. 93 3062 (1971). These authors chloromethylated slightly cross-linked polystyrene and reacted the resulting chlorine-containing polymer with lithium diphenyl-phosphine to produce a ligand-substituted polystyrene. Combination of the modified polymer with Wilkinson's catalyst, by coordination, produced an active, readily isolated, heterogeneous catalyst. Utility as a hydrogenation catalyst was demonstrated.
Allum et al in U.S. Pat. No. 3,652,678 and Young in U.S. Pat. No. 3,987,009 disclosed similar heterogeneous catalysts employing various insolubilizing polymers.
Allen in U.S. Pat. No. 3,998,887 disclosed catalysts of similar type which comprised a polymer derived from p-styryldiethylphosphine.
Trevillyan in U.S. Pat. No. 4.045,493 disclosed such catalysts comprising a polyphenylene polymer backbone and pendant diphenylphosphine ligand groups. Such catalysts are reported to be more thermally stable under reaction conditions than are similar catalysts derived from polyvinyl chloride and polystyrene.
British Pat. No. 1,517,552 taught a process for preparing other catalysts insolubilized by covalent attachment to various polymers. The catalysts of this patent are characterized by diphosphine bidentate ligands. Increased reaction specificity was claimed for such catalysts.
Other inventors have produced insoluble catalysts by attachment of ligand groups to inorganic solids. For example, Oswald et al in U.S. Pat. No. 3,907,852 disclosed a process for preparing heterogeneous rhodium catalysts comprising silylhydrocarbyl phosphine ligands attached to silica and metal oxides.
Allum et al in U.S. Pat. No. 3,832,404 disclosed a hydroformylation process employing various catalysts, among others a rhodium catalyst comprising a monodentate phosphine ligand attached to inorganic solids containing a hydroxyl group. Silica was a preferred solid. The catalysts were prepared by addition of diphenylphosphine to triethoxyvinyl silane to form an intermediate which was combined, for example, with cyclo-octadiene rhodium chloride to produce a rhodium complex. The complex was attached to silica by ester exchange.